Official nominations for candidates to replace Michael Howard as Conservative leader have opened.
Mr Howard has not named his choice of successor
The contest began as Mr Howard formally resigned by letter to Sir Michael Spicer, chairman of the 1922 Committee of Tory MPs.
Five candidates have declared they will run for leader, with David Cameron taking over from David Davis as the favourite at the bookmakers.
Mr Howard stays on as caretaker until a replacement is named on 6 December.
Nominations close at midday next Thursday.
David Cameron 5/6
David Davis 7/4
Ken Clarke 11/2
Liam Fox 12/1
Sir Malcolm Rifkind 80/1
Mr Howard first announced he would go shortly after the general election in May, when the Conservatives won 198 seats, a result he described as not good enough.
This week's annual party conference in Blackpool saw each declared candidate - Sir Malcolm Rifkind, David Cameron, Ken Clarke, David Davis and Liam Fox - put their case to members.
In his speech on Thursday, Mr Howard said he had feared the event going "pear shaped".
He added: "Of course we need discussion and debate. But let's not be offensive about each other.
"Let's not run down our party. Let's show we can elect a new leader without bitterness."
Mr Davis remains the candidate with the most declared backers among MPs, but his campaign appears to have lost momentum after his conference was criticised in the press as "lacklustre".
Sir Malcolm Rifkind said his opponent must be "very worried".
But Mr Davis said he remained the frontrunner and that he would not be bowed by criticism.
The party's deputy leader, Michael Ancram, has revealed he is supporting Sir Malcolm's bid.
Meanwhile, David Cameron's team claims to be picking up more support from MPs, as an Evening Standard poll of 100 party members put him ahead of his rivals.
Conservative MPs will narrow the candidates down to two, before a vote by party members around the UK.
Mr Howard has not named his favoured successor.
Meanwhile, shadow culture secretary Theresa May has urged the Conservative Party to take "radical action" to win back women voters.